OK, to check that we’re all on the same page, let’s state this: although blanket statements like “south of 8”, “north of 8”, etc are obviously incorrect, I would say that it is true that San Diego has a fair share of distressed neighborhoods (wherever they may be located).
I think that San Diego’s median is lower than that of VC and OC precisely because of that. Although I’m sure OC and VC have their own bad neighborhoods, I would argue that San Diego probably has a higher share of them. Those who know more about SoCal demographics, please feel free to correct me if I’m wrong.